1. Field of the Invention
The present invention relates generally to gas blade spacers that are disposed beneath dovetail roots of blades within dovetail slots in gas turbine engine assemblies and, more particularly, to such spacers for fan assemblies having fan blades with circular arc dovetail roots that mate in circular arc dovetail slots in a disk of a fan rotor.
2. Discussion of the Background Art
A turbofan gas turbine engine used for powering an aircraft in flight includes a fan assembly having a plurality of circumferentially spaced apart fan blades extending radially outwardly from a rotor disk. Ambient airflow is channeled between the blades and pressurized, thereby, generating thrust for powering the aircraft in flight. The fan assembly typically includes a plurality of circumferentially spaced apart fan blades, each having a dovetail root disposed in a complementary, axially extending dovetail groove or slot in a perimeter or rim of a rotor disk. The dovetail slots are defined by dovetail posts and are complementary in configuration with the blade dovetail roots for radially retaining the blades to the rotor disk. The blades are also axially retained in the rotor disk to prevent axial movement of the blades in the upstream and downstream directions. A spacer fills the balance of the space below the blade root within slot.
During a bladeout event, a blade or portion of blade is released and impacts the first trailing blade adjacent the damaged blade causing the first trailing blade to rotate circumferentially. The present invention is particularly useful for fan assemblies with circular arc dovetail roots and slots. This makes the dovetail load up on point locations which jeopardized the integrity of the dovetail. The blade needs to be prevented from rotating too much and loading the corners up. When the blade tends to rotate, the spacer gets pinched between the bottom of the blade root and the bottom of the slot in the disk, thus, preventing rotation. The rotational moment is shared by a majority of the pressure face instead of on the corner points of the dovetail root.
A fan disk assembly for a low radius hub design incorporating a circular arc dovetail root and slot to ensure an adequate footprint and load path into the disk has been developed. This design is used for increasing the airflow through the fan blades to increase the thrust without increasing or holding to a limit of a tip of the fan blade. An inner flowpath boundary, often referred to as the hub, is moved radially inwardly from an existing engine design or the engine is originally designed to have, what is referred to as, a low radius hub. Conventionally, a radial transition portion is a transition from a curved blade section at the flowpath to a straight shank at the top of the dovetail. Due to the low inner diameter of the flow path, the radial transition portion of the fan blade from the aerodynamic or curved portion of the blade to the dovetail root is significantly shortened. It is highly desirable to have an improved spacer for a low radius hub design which incorporates a circular arc dovetail root and slot to ensure adequate blade retention for the first trailing blade adjacent the damaged blade during a bladeout event.
A gas turbine engine blade spacer has an axially extending backbone, spaced apart forward, mid and aft dovetail lands, respectively, disposed along the backbone, the backbone and the forward, mid, and aft dovetail lands having bottom curved backbone surfaces. Each of the forward, mid and aft dovetail lands has a riser that extends above the backbone and has a riser flat top. In the exemplary embodiment disclosed herein, a spacer tab extends generally axially forward of the forward land and includes intersecting axially and radially extending tab apertures. A void extends around the backbone and between the forward and aft dovetail lands and the void is filled with an elastomeric material. The spacer has a constant shape and size cross-section between the forward and aft dovetail lands.
The invention has a particular use with circular arc dovetail slots and roots for which the spacer is a circular arc shaped spacer and the backbone, and the forward, mid and aft dovetail lands are curved along a circular arc normal to and about a radial axis. The spacer tab has a rectangular cross-section, extends axially out of a forward face of the forward land, and has a tab flat top that is co-planar with the riser flat tops of the risers.
In one particular embodiment, the invention is a spacer in a gas turbine engine rotor disk assembly having a number of annular hubs circumscribed about a centerline, each of the hubs connected to a disk rim by a web, and a plurality of circumferentially spaced apart dovetail slots disposed through the rim. The dovetail slots extend circumferentially between disk posts, axially from a forward end to an aft end of the rim, and radially inwardly from a disk outer surface of the rim. A plurality of fan blades have dovetail roots which are disposed in the dovetail slots and corresponding ones of the blade spacers which are disposed in the dovetail slots between a dovetail slot bottom wall and an axially extending root bottom surface of each of the dovetail roots. Circumferentially extending annular burst slots extend radially through the rim into the dovetail slots between each adjacent pair of the webs. The forward, mid, and aft dovetail lands, respectively, are located along the backbone such that the burst slots are located between the forward, mid, and aft dovetail lands.
In yet a more particular embodiment of the invention, pairs of circumferentially oppositely facing retaining slots extend through overhangs of circumferentially adjacent pairs of the disk posts at an axial location where the overhangs begin extending axially forward from the rim. Retainers are disposed in the pairs of retaining slots and extend across the dovetail slot so as to axially retain the dovetail roots in the dovetail slots. Each of the retainers is radially supported by a corresponding one of the spacers and each of the retainers includes a rectangular slot through which is disposed a corresponding one of the spacer tabs. Each retainer includes a shelf radially below the slot and upon which the spacer tab rests. A radially extending shelf aperture is disposed through the shelf and aligned with the radially extending tab aperture. A spacer bolt having a spacer bolt head and a threaded spacer bolt shank is disposed through the shelf aperture and the radially extending tab aperture such that the spacer bolt head engages the shelf. A spacer nut is threadingly secured on the spacer bolt shank such that the spacer nut engages the spacer tab.